Macrophage memories of early-life injury drive neonatal nociceptive priming.

The developing peripheral nervous and immune systems are functionally distinct from those of adults. These systems are vulnerable to early-life injury, which influences outcomes related to nociception following subsequent injury later in life (i.e., "neonatal nociceptive priming"). The underpinnings of this phenomenon are unclear, although previous work indicates that macrophages are trained by inflammation and injury. Our findings show that macrophages are both necessary and partially sufficient to drive neonatal nociceptive priming, possibly due to a long-lasting remodeling in chromatin structure. The p75 neurotrophic factor receptor is an important effector in regulating neonatal nociceptive priming through modulation of the inflammatory profile of rodent and human macrophages. This "pain memory" is long lasting in females and can be transferred to a naive host to alter sex-specific pain-related behaviors. This study reveals a mechanism by which acute, neonatal post-surgical pain drives a peripheral immune-related predisposition to persistent pain following a subsequent injury.

Utilization of a Histoplasma capsulatum zinc reporter reveals the complexities of fungal sensing of metal deprivation.

Histoplasma capsulatum is a dimorphic fungal pathogen acquired via inhalation of soil-resident spores. Upon exposure to mammalian body temperatures, these fungal elements transform into yeasts that reside primarily within phagocytes. Macrophages (MΦ) provide a permissive environment for fungal replication until T cell-dependent immunity is engaged. MΦ activated by granulocyte macrophage colony stimulating factor (GM-CSF) induces metallothioneins (MTs) that bind zinc (Zn) and deprive yeast cells of labile Zn, thereby disabling fungal growth. Prior work demonstrated that the zinc transporter, ZRT2, was important for fungal survival in vivo. Hence, we constructed a yeast cell reporter strain that expresses green fluorescent protein (GFP) under control of the ZRT2 zinc-regulated promoter. This reporter accurately responds to a medium devoid of Zn. ZRT2 expression increased in GM-CSF, but not interferon-γ, stimulated MΦ. To examine the in vivo response, we infected mice with a reporter yeast strain and assessed ZRT2 expression at 0, 3, 7, and 14 days post-infection (dpi). ZRT2 expression minimally increased at 3 dpi and peaked at 7 dpi, corresponding with the onset of adaptive immunity. We discovered that the major MΦ populations that restrict Zn from the fungus are interstitial MΦ and exudate MΦ. Neutralizing GM-CSF blunted the control of infection but unexpectedly increased ZRT2 expression. This increase was dependent on another cytokine that activates MΦ to control H. capsulatum replication, M-CSF. These findings illustrate the reporter's ability to sense Zn in vitro and in vivo and correlate ZRT2 expression with GM-CSF and M-CSF activation of MΦ.IMPORTANCEPhagocytes use an arsenal of defenses to control the replication of Histoplasma yeasts, one of which is the limitation of trace metals. On the other hand, H. capsulatum combats metal restriction by upregulating metal importers such as the Zn importer ZRT2. This transporter contributes to H. capsulatum pathogenesis upon activation of adaptive immunity. We constructed a fluorescent ZRT2 transcriptional reporter to probe H. capsulatum Zn sensing during infection and exposed the role for M-CSF activation of macrophages when GM-CSF is absent. These data highlight the ways in which fungal pathogens sense metal deprivation in vivo and reveal the potential of metal-sensing reporters. The work adds a new dimension to study how intracellular pathogens sense and respond to the changing environments of the host.

Utilization of a Histoplasma capsulatum zinc reporter reveals the complexities of fungal sensing of metal deprivation.

Histoplasma capsulatum is a dimorphic fungal pathogen acquired via inhalation of soil-resident spores. Upon exposure to mammalian body temperatures, these fungal elements transform into yeasts that reside primarily within phagocytes. Macrophages (MΦ) provide a permissive environment for fungal replication until T cell-dependent immunity is engaged. MΦ activated by granulocyte-MΦ colony stimulating factor (GM-CSF) induce metallothioneins (MTs) that bind zinc (Zn) and deprive yeast cells of labile Zn, thereby disabling fungal growth. Prior work demonstrated that the high affinity zinc importer, ZRT2, was important for fungal survival in vivo. Hence, we constructed a yeast cell reporter strain that expresses green fluorescent protein (GFP) under the control of this importer. This reporter accurately responds to medium devoid of Zn. ZRT2 expression increased (∼5-fold) in GM-CSF, but not interferon-γ, stimulated MΦ. To examine the in vivo response, we infected mice with reporter yeasts and assessed ZRT2 expression at 0-, 3-, 7-, and 14-days post-infection (dpi). ZRT2 expression minimally increased at 3-dpi and peaked on 7-dpi, corresponding with onset of adaptive immunity. We discovered that the major phagocyte populations that restrict Zn to the fungus are interstitial MΦ and exudate MΦ. Neutralizing GM-CSF blunted control of infection but unexpectedly increased ZRT2 expression. This increase was dependent on another cytokine that activates MΦ to control H. capsulatum replication, M-CSF. These findings illustrate the reporter's ability to sense Zn in vitro and in vivo and correlate ZRT2 activity with GM-CSF and M-CSF activation of MΦ. Importance: Phagocytes use an arsenal of defenses to control replication of Histoplasma yeasts, one of which is limitation of trace metals. On the other hand, H. capsulatum combats metal restriction by upregulating metal importers such as the Zn importer ZRT2. This transporter contributes to H. capsulatum pathogenesis upon activation of adaptive immunity. We constructed a fluorescent ZRT2 reporter to probe H. capsulatum Zn sensing during infection and exposed a role for M-CSF activation of macrophages when GM-CSF is absent. These data highlight the ways in which fungal pathogens sense metal deprivation in vivo and reveal the potential of metal-sensing reporters. The work adds a new dimension to studying how intracellular pathogens sense and respond to the changing environments of the host.

Macrophage epigenetic memories of early life injury drive neonatal nociceptive priming.

The developing peripheral nervous and immune systems are functionally distinct from adults. These systems are vulnerable to early life injury, which influences outcomes related to nociception following subsequent injury later in life (neonatal nociceptive priming). The underpinnings of this phenomenon are largely unknown, although previous work indicates that macrophages are epigenetically trained by inflammation and injury. We found that macrophages are both necessary and partially sufficient to drive neonatal nociceptive priming possibly due to a long-lasting epigenetic remodeling. The p75 neurotrophic factor receptor (NTR) was an important effector in regulating neonatal nociceptive priming through modulation of the inflammatory profile of rodent and human macrophages. This pain memory was long lasting in females and could be transferred to a naive host to alter sex-specific pain-related behaviors. This study reveals a novel mechanism by which acute, neonatal post-surgical pain drives a peripheral immune-related predisposition to persistent pain following a subsequent injury.

Pro-Inflammatory Alterations of Circulating Monocytes in Latent Tuberculosis Infection.

Background: Latent tuberculosis infection (LTBI) has been associated with increased cardiovascular risk. We investigated the activation and pro-inflammatory profile of monocytes in individuals with LTBI and their association with coronary artery disease (CAD). Methods: Individuals 40-70 years old in Lima, Peru, underwent QuantiFERON-TB testing to define LTBI, completed a coronary computed tomography angiography to evaluate CAD, and provided blood for monocyte profiling using flow cytometry. Cells were stimulated with lipopolysaccharide to assess interleukin-6 (IL-6) and tumor necrosis factor (TNF)-α responses. Results: The clinical characteristics of the LTBI (n = 28) and non-LTBI (n = 41) groups were similar. All monocyte subsets from LTBI individuals exhibited higher mean fluorescence intensity (MFI) of CX3CR1 and CD36 compared with non-LTBI individuals. LTBI individuals had an increased proportion of nonclassical monocytes expressing IL-6 (44.9 vs 26.9; P = .014), TNF-α (62.3 vs 35.1; P = .014), and TNF-α+IL-6+ (43.2 vs 36.6; P = .042). Among LTBI individuals, CAD was associated with lower CX3CR1 MFI on classical monocytes and lower CD36 MFI across all monocyte subsets. In multivariable analyses, lower CD36 MFI on total monocytes (b = -0.17; P = .002) and all subsets remained independently associated with CAD in LTBI. Conclusions: Individuals with LTBI have distinct monocyte alterations suggestive of an exacerbated inflammatory response and tissue migration. Whether these alterations contribute to cardiovascular disease pathogenesis warrants further investigation.

Notch regulates Histoplasma capsulatum clearance in mouse lungs during innate and adaptive immune response phases in primary infection.

The clearance of the pathogenic fungus, Histoplasma capsulatum, requires cooperation between innate and adaptive immunity. Since this organism is inhaled, lung macrophages and dendritic cells (DCs) are the first lines of defense. Moreover, DCs act as APCs to drive the education of type 1 Th cells to produce IFNγ, which contributes to the final elimination of H. capsulatum. In this study, we explored the importance of Notch signaling in host defenses using a mouse model of pulmonary histoplasmosis. We found up-regulation of Notch ligands (NLs) and Notch receptors (NRs) on phagocytes and IFNγ+ CD4+ T cells upon infection in lungs and lymph nodes. To ascertain the influence of Notch on the course of infection, we used a gamma-secretase inhibitor (GSI), LY-411,575, which inhibits NR downstream signaling. This compound impaired fungal clearance when given at the time of infection or 7 days after infection. However, GSI did not impact fungal clearance in mice with preexisting immunity. The dampened host defenses were associated with reduced differentiation and maturation of monocyte-derived DCs and elevatmonocyte-derived macrophage and alveolar macrophage polarization to M2. Our study reveals the critical nature of Notch signaling in maintaining control of this infectious agent.

Restraint of Fumarate Accrual by HIF-1α Preserves miR-27a-Mediated Limitation of Interleukin 10 during Infection of Macrophages by Histoplasma capsulatum.

Hypoxia-inducible factor 1α (HIF-1α) regulates the immunometabolic phenotype of macrophages, including the orchestration of inflammatory and antimicrobial processes. Macrophages deficient in HIF-1α produce excessive quantities of the anti-inflammatory cytokine interleukin 10 (IL-10) during infection with the intracellular fungal pathogen Histoplasma capsulatum (R. A. Fecher, M. C. Horwath, D. Friedrich, J. Rupp, G. S. Deepe, J Immunol 197:565-579, 2016, https://doi.org/10.4049/jimmunol.1600342). Thus, the macrophage fails to become activated in response to proinflammatory cytokines and remains the intracellular niche of the pathogen. Here, we identify the tricarboxylic acid (TCA) cycle metabolite fumarate as the driver of IL-10 during macrophage infection with H. capsulatum in the absence of HIF-1α. Accumulation of fumarate reduced expression of a HIF-1α-dependent microRNA (miRNA), miR-27a, known to mediate decay of Il10 mRNA. Inhibition of fumarate accrual in vivo limited IL-10 and fungal growth. Our data demonstrate the critical role of HIF-1α in shaping appropriate TCA cycle activity in response to infection and highlight the consequences of a dysregulated immunometabolic response. IMPORTANCE Histoplasma capsulatum and related Histoplasma species are intracellular fungal pathogens endemic to broad regions of the globe, including the Americas, Africa, and Asia. While most infections resolve with mild or no symptoms, failure of the host to control fungal growth produces severe disease. Previously, we reported that loss of a key transcriptional regulator, hypoxia-inducible factor 1α (HIF-1α), in macrophages led to a lethal failure to control growth of Histoplasma (R. A. Fecher, M. C. Horwath, D. Friedrich, J. Rupp, G. S. Deepe, J Immunol 197:565-579, 2016, https://doi.org/10.4049/jimmunol.1600342). Inhibition of phagocyte activation due to excessive interleukin 10 by HIF-1α-deficient macrophages drove this outcome. In this study, we demonstrate that HIF-1α maintains contextually appropriate TCA cycle metabolism within Histoplasma-infected macrophages. The absence of HIF-1α results in excessive fumarate production that alters miRNA-27a regulation of interleukin-10. HIF-1α thus preserves the capacity of macrophages to transition from a permissive intracellular niche to the site of pathogen killing.

A metabolic inhibitor arms macrophages to kill intracellular fungal pathogens by manipulating zinc homeostasis.

Macrophages deploy numerous strategies to combat invasion by microbes. One tactic is to restrict acquisition of diverse nutrients, including trace metals, a process termed nutritional immunity. Intracellular pathogens adapt to a resource-poor environment by marshaling mechanisms to harvest nutrients. Carbon acquisition is crucial for pathogen survival; compounds that reduce availability are a potential strategy to control intracellular replication. Treatment of macrophages with the glucose analog 2-deoxy-D-glucose (2-DG) armed phagocytes to eliminate the intracellular fungal pathogen Histoplasma capsulatum in vitro and in vivo. Killing did not rely on altering access to carbon-containing molecules or changes in ATP, ER stress, or autophagy. Unexpectedly, 2-DG undermined import of exogenous zinc into macrophages, decreasing the quantity of cytosolic and phagosomal zinc. The fungus perished as a result of zinc starvation. This change in metal ingress was not ascribed to a defect in a single importer; rather, there was a collective impairment in transporter activity. This effect promoted the antifungal machinery of macrophages and expanded the complexity of 2-DG activities far beyond manipulating glycolysis. Mechanistic metabolic studies employing 2-DG will have to consider its effect on zinc transport. Our preclinical data support consideration of this agent as a possible adjunctive therapy for histoplasmosis.

Adipocyte inflammation and pathogenesis of viral pneumonias: an overlooked contribution.

Epidemiological evidence establishes obesity as an independent risk factor for increased susceptibility and severity to viral respiratory pneumonias associated with H1N1 influenza and SARS-CoV-2 pandemics. Given the global obesity prevalence, a better understanding of the mechanisms behind obese susceptibility to infection is imperative. Altered immune cell metabolism and function are often perceived as a key causative factor of dysregulated inflammation. However, the contribution of adipocytes, the dominantly altered cell type in obesity with broad inflammatory properties, to infectious disease pathogenesis remains largely ignored. Thus, skewing of adipocyte-intrinsic cellular metabolism may lead to the development of pathogenic inflammatory adipocytes, which shape the overall immune responses by contributing to either premature immunosenescence, delayed hyperinflammation, or cytokine storm in infections. In this review, we discuss the underappreciated contribution of adipocyte cellular metabolism and adipocyte-produced mediators on immune system modulation and how such interplay may modify disease susceptibility and pathogenesis of influenza and SARS-CoV-2 infections in obese individuals.

Regulation of the Mitochondrion-Fatty Acid Axis for the Metabolic Reprogramming of Chlamydia trachomatis during Treatment with ß-Lactam Antimicrobials.

Infection with the obligate intracellular bacterium Chlamydia trachomatis is the most common bacterial sexually transmitted disease worldwide. Since no vaccine is available to date, antimicrobial therapy is the only alternative in C. trachomatis infection. However, changes in chlamydial replicative activity and the occurrence of chlamydial persistence caused by diverse stimuli have been proven to impair treatment effectiveness. Here, we report the mechanism for C. trachomatis regulating host signaling processes and mitochondrial function, which can be used for chlamydial metabolic reprogramming during treatment with ß-lactam antimicrobials. Activation of signal transducer and activator of transcription 3 (STAT3) is a well-known host response in various bacterial and viral infections. In C. trachomatis infection, inactivation of STAT3 by host protein tyrosine phosphatases increased mitochondrial respiration in both the absence and presence of ß-lactam antimicrobials. However, during treatment with ß-lactam antimicrobials, C. trachomatis increased the production of citrate as well as the activity of host ATP-citrate lyase involved in fatty acid synthesis. Concomitantly, chlamydial metabolism switched from the tricarboxylic acid cycle to fatty acid synthesis. This metabolic switch was a unique response in treatment with ß-lactam antimicrobials and was not observed in gamma interferon (IFN-γ)-induced persistent infection. Inhibition of fatty acid synthesis was able to attenuate ß-lactam-induced chlamydial persistence. Our findings highlight the importance of the mitochondrion-fatty acid interplay for the metabolic reprogramming of C. trachomatis during treatment with ß-lactam antimicrobials.IMPORTANCE The mitochondrion generates most of the ATP in eukaryotic cells, and its activity is used for controlling the intracellular growth of Chlamydia trachomatis Furthermore, mitochondrial activity is tightly connected to host fatty acid synthesis that is indispensable for chlamydial membrane biogenesis. Phospholipids, which are composed of fatty acids, are the central components of the bacterial membrane and play a crucial role in the protection against antimicrobials. Chlamydial persistence that is induced by various stimuli is clinically relevant. While one of the well-recognized inducers, ß-lactam antimicrobials, has been used to characterize chlamydial persistence, little is known about the role of mitochondria in persistent infection. Here, we demonstrate how C. trachomatis undergoes metabolic reprogramming to switch from the tricarboxylic acid cycle to fatty acid synthesis with promoted host mitochondrial activity in response to treatment with ß-lactam antimicrobials.

CD4+CTLs in Fibrosing Mediastinitis Linked to Histoplasma capsulatum.

Although fibrotic disorders are frequently assumed to be linked to TH2 cells, quantitative tissue interrogation studies have rarely been performed to establish this link and certainly many fibrotic diseases do not fall within the type 2/allergic disease spectrum. We have previously linked two human autoimmune fibrotic diseases, IgG4-related disease and systemic sclerosis, to the clonal expansion and lesional accumulation of CD4+CTLs. In both these diseases TH2 cell accumulation was found to be sparse. Fibrosing mediastinitis linked to Histoplasma capsulatum infection histologically resembles IgG4-related disease in terms of the inflammatory infiltrate and fibrosis, and it provides an example of a fibrotic disease of infectious origin in which the potentially profibrotic T cells may be induced and reactivated by fungal Ags. We show in this study that, in this human disease, CD4+CTLs accumulate in the blood, are clonally expanded, infiltrate into disease lesions, and can be reactivated in vitro by H. capsulatum Ags. TH2 cells are relatively sparse at lesional sites. These studies support a general role for CD4+CTLs in inflammatory fibrosis and suggest that fibrosing mediastinitis is an Ag-driven disease that may provide important mechanistic insights into the pathogenesis of idiopathic fibrotic diseases.

GM-CSF and IL-33 Orchestrate Polynucleation and Polyploidy of Resident Murine Alveolar Macrophages in a Murine Model of Allergic Asthma.

Allergic asthma is a chronical pulmonary disease with high prevalence. It manifests as a maladaptive immune response to common airborne allergens and is characterized by airway hyperresponsiveness, eosinophilia, type 2 cytokine-associated inflammation, and mucus overproduction. Alveolar macrophages (AMs), although contributing to lung homeostasis and tolerance to allergens at steady state, have attracted less attention compared to professional antigen-presenting and adaptive immune cells in their contributions. Using an acute model of house dust mite-driven allergic asthma in mice, we showed that a fraction of resident tissue-associated AMs, while polarizing to the alternatively activated M2 phenotype, exhibited signs of polynucleation and polyploidy. Mechanistically, in vitro assays showed that only Granulocyte-Macrophage Colony Stimulating Factor and interleukins IL-13 and IL-33, but not IL-4 or IL-5, participate in the establishment of this phenotype, which resulted from division defects and not cell-cell fusion as shown by microscopy. Intriguingly, mRNA analysis of AMs isolated from allergic asthmatic lungs failed to show changes in the expression of genes involved in DNA damage control except for MafB. Altogether, our data support the idea that upon allergic inflammation, AMs undergo DNA damage-induced stresses, which may provide new unconventional therapeutical approaches to treat allergic asthma.

Crosstalk Between Autophagy and Hypoxia-Inducible Factor-1α in Antifungal Immunity.

Modern medicine is challenged by several potentially severe fungal pathogens such as Aspergillus fumigatus, Candida albicans, or Histoplasma capsulatum. Though not all fungal pathogens have evolved as primary pathogens, opportunistic pathogens can still cause fatal infections in immuno-compromised patients. After infection with these fungi, the ingestion and clearance by innate immune cells is an important part of the host immune response. Innate immune cells utilize two different autophagic pathways, the canonical pathway and the non-canonical pathway, also called microtubule-associated protein 1A/1B-light chain 3 (LC3) -associated pathway (LAP), to clear fungal pathogens from the intracellular environment. The outcome of autophagy-related host immune responses depends on the pathogen and cell type. Therefore, the understanding of underlying molecular mechanisms of autophagy is crucial for the development and improvement of antifungal therapies. One of those molecular mechanisms is the interaction of the transcription-factor hypoxia-inducible factor 1α (HIF-1α) with the autophagic immune response. During this review, we will focus on a comprehensive overview of the role of autophagy and HIF-1α on the outcome of fungal infections.

IL-10-producing Tfh cells accumulate with age and link inflammation with age-related immune suppression.

Aging results in profound immune dysfunction, resulting in the decline of vaccine responsiveness previously attributed to irreversible defects in the immune system. In addition to increased interleukin-6 (IL-6), we found aged mice exhibit increased systemic IL-10 that requires forkhead box P3-negative (FoxP3-), but not FoxP3+, CD4+T cells. Most IL-10-producing cells manifested a T follicular helper (Tfh) phenotype and required the Tfh cytokines IL-6 and IL-21 for their accrual, so we refer to them as Tfh10 cells. IL-21 was also required to maintain normal serum levels of IL-6 and IL-10. Notably, antigen-specific Tfh10 cells arose after immunization of aged mice, and neutralization of IL-10 receptor signaling significantly restored Tfh-dependent antibody responses, whereas depletion of FoxP3+ regulatory and follicular regulatory cells did not. Thus, these data demonstrate that immune suppression with age is reversible and implicate Tfh10 cells as an intriguing link between "inflammaging" and impaired immune responses with age.

Metabolism of Gluconeogenic Substrates by an Intracellular Fungal Pathogen Circumvents Nutritional Limitations within Macrophages.

Microbial pathogens exploit host nutrients to proliferate and cause disease. Intracellular pathogens, particularly those exclusively living in the phagosome such as Histoplasma capsulatum, must adapt and acquire nutrients within the nutrient-limited phagosomal environment. In this study, we investigated which host nutrients could be utilized by Histoplasma as carbon sources to proliferate within macrophages. Histoplasma yeasts can grow on hexoses and amino acids but not fatty acids as the carbon source in vitro Transcriptional analysis and metabolism profiling showed that Histoplasma yeasts downregulate glycolysis and fatty acid utilization but upregulate gluconeogenesis within macrophages. Depletion of glycolysis or fatty acid utilization pathways does not prevent Histoplasma growth within macrophages or impair virulence in vivo However, loss of function in Pck1, the enzyme catalyzing the first committed step of gluconeogenesis, impairs Histoplasma growth within macrophages and severely attenuates virulence in vivo, indicating that Histoplasma yeasts rely on catabolism of gluconeogenic substrates (e.g., amino acids) to proliferate within macrophages.IMPORTANCEHistoplasma is a primary human fungal pathogen that survives and proliferates within host immune cells, particularly within the macrophage phagosome compartment. The phagosome compartment is a nutrient-limited environment, requiring Histoplasma yeasts to be able to assimilate available carbon sources within the phagosome to meet their nutritional needs. In this study, we showed that Histoplasma yeasts do not utilize fatty acids or hexoses for growth within macrophages. Instead, Histoplasma yeasts consume gluconeogenic substrates to proliferate in macrophages. These findings reveal the phagosome composition from a nutrient standpoint and highlight essential metabolic pathways that are required for a phagosomal pathogen to proliferate in this intracellular environment.

Type I Interferons Rule with an Iron Fist.

Pathogens rely on nutrient assimilation, particularly essential metal incorporation, to successfully survive in the host. In this issue of Cell Host & Microbe, Riedelberger et al. (2020) convincingly demonstrate that type I interferons (IFNs-I) promote dysregulation of iron homeostasis in macrophages upon infection with Candida glabrata and exacerbate infection.

Mycobacterium bovis Bacille-Calmette-Guérin Infection Aggravates Atherosclerosis.

Tuberculosis has been associated with increased risk of atherosclerotic cardiovascular disease. To examine whether mycobacterial infection exacerbates atherosclerosis development in experimental conditions, we infected low-density lipoprotein receptor knockout (Ldlr-/-) mice with Mycobacterium bovis Bacille-Calmette-Guérin (BCG), an attenuated strain of the Mycobacterium tuberculosis complex. Twelve-week old male Ldlr-/- mice were infected with BCG (0.3-3.0x106 colony-forming units) via the intranasal route. Mice were subsequently fed a western-type diet containing 21% fat and 0.2% cholesterol for up to 16 weeks. Age-matched uninfected Ldlr-/- mice fed with an identical diet served as controls. Atherosclerotic lesions in aorta were examined using Oil Red O staining. Changes induced by BCG infection on the immunophenotyping profile of circulating T lymphocytes and monocytes were assessed using flow cytometry. BCG infection increased atherosclerotic lesions in en face aorta after 8 weeks (plaque ratio; 0.021±0.01 vs. 0.013±0.01; p = 0.011) and 16 weeks (plaque ratio, 0.15±0.13 vs. 0.06±0.02; p = 0.003). No significant differences in plasma cholesterol or triglyceride levels were observed between infected and uninfected mice. Compared to uninfected mice, BCG infection increased systemic CD4/CD8 T cell ratio and the proportion of Ly6Clow non-classical monocytes at weeks 8 and 16. Aortic plaque ratios correlated with CD4/CD8 T cell ratios (Spearman's rho = 0.498; p = 0.001) and the proportion of Ly6Clow non-classical monocytes (Spearman's rho = 0.629; p < 0.001) at week 16. In conclusion, BCG infection expanded the proportion of CD4+ T cell and Ly6Clow monocytes, and aggravated atherosclerosis formation in the aortas of hyperlipidemic Ldlr-/- mice. Our results indicate that mycobacterial infection is capable of enhancing atherosclerosis development.

Metallothionein 3 Controls the Phenotype and Metabolic Programming of Alternatively Activated Macrophages.

Alternatively activated (M2) macrophages promote wound healing but weaken antimicrobial defenses. The mechanisms that enforce macrophage divergence and dictate the phenotypic and metabolic characteristics of M2 macrophages remain elusive. We show that alternative activation with interleukin (IL)-4 induces expression of metallothionein 3 (MT3) that regulates macrophage polarization and function. MT3 was requisite for metabolic reprograming in IL-4-stimulated macrophages or M(IL-4) macrophages to promote mitochondrial respiration and suppress glycolysis. MT3 fostered an M(IL-4) phenotype, suppressed hypoxia inducible factor (HIF)1α activation, and thwarted the emergence of a proinflammatory M1 program in macrophages. MT3 deficiency augmented macrophage plasticity, resulting in enhanced interferon γ (IFNγ) responsiveness and a dampened M(IL-4) phenotype. Thus, MT3 programs the phenotype and metabolic fate of M(IL-4) macrophages.

The HIF-1α/LC3-II Axis Impacts Fungal Immunity in Human Macrophages.

The fungal pathogen Histoplasma capsulatum causes a spectrum of disease, ranging from local pulmonary infection to disseminated disease. The organism seeks residence in macrophages, which are permissive for its survival. Hypoxia-inducible factor 1α (HIF-1α), a principal regulator of innate immunity to pathogens, is necessary for macrophage-mediated immunity to H. capsulatum in mice. In the present study, we analyzed the effect of HIF-1α in human macrophages infected with this fungus. HIF-1α stabilization was detected in peripheral blood monocyte-derived macrophages at 2 to 24 h after infection with viable yeast cells. Further, host mitochondrial respiration and glycolysis were enhanced. In contrast, heat-killed yeasts induced early, but not later, stabilization of HIF-1α. Since the absence of HIF-1α is detrimental to host control of infection, we asked if large amounts of HIF-1α protein, exceeding those induced by H. capsulatum, altered macrophage responses to this pathogen. Exposure of infected macrophages to an HIF-1α stabilizer significantly reduced recovery of H. capsulatum from macrophages and produced a decrement in mitochondrial respiration and glycolysis compared to those of controls. We observed recruitment of the autophagy-related protein LC3-II to the phagosome, whereas enhancing HIF-1α reduced phagosomal decoration. This finding suggested that H. capsulatum exploited an autophagic process to survive. In support of this assertion, inhibition of autophagy activated macrophages to limit intracellular growth of H. capsulatum Thus, enhancement of HIF-1α creates a hostile environment for yeast cells in human macrophages by interrupting the ability of the pathogen to provoke host cell autophagy.